Composite pipe

ABSTRACT

A sleeved composite pipe or piling structure formed of an elongated polyethylene pipe or tube of high-density polyethylene (HDPE) or another polyethylene material installed over a substantially rigid and incompressible hollow metal pipe or solid wood core having an outer diameter that is the same or slightly larger than a normal inside diameter of the polyethylene pipe or tube when measured in a relaxed state at ambient temperature. The polyethylene pipe or tube is, for example, a HDPE 3408 material formed of virgin PE 3408 resin as specified in ASTM D3350 with UV protection, and the pipe is produced to ASTM A-3408. The metal pipe core can be ferrous or nonferrous pipe.

This application is a Continuation and claims priority benefit ofcopending parent U.S. patent application Ser. No. 11/904,873 filed inthe name of William R. Watson, the common inventor hereof, on Sep. 28,2007 now U.S. Pat. No. 7,987,576, the complete disclosure of which isincorporated herein by reference, which is a Divisional and claimspriority benefit of parent U.S. patent application Ser. No. 11/132,928filed in the name of William R. Watson, the common inventor hereof, onMay 18, 2005, now U.S. Pat. No. 7,563,496 issued Jul. 21, 2009, thecomplete disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a composite pipe device, and inparticular to a sleeve of high-density polyethylene (HDPE) pipecompression fit over a metal pipe or solid core.

BACKGROUND OF THE INVENTION

Corrosion has always been a problem for metal pipe, especially thoseburied underground or driven into the sea floor for use as pilings. Evengalvanized pipe corrodes over time as the thin galvanic coating wearsaway. Different composite pipe devices are also known, including pipedevices having a plastic shell extruded over the pipe. However, knownplastic-metal composite pipe is formed of recycled material extrudedover pipe of undetermined structural quality, which results in ancomposite pipe of unknown quality that requires further testing andcertification for use in many industrial applications.

SUMMARY OF THE INVENTION

The present invention overcomes the manufacturing and load capacitylimitations of the prior art by providing a sleeved or “jacketed”composite pipe structure formed of an elongated polyethylene pipe ortube of high-density polyethylene (HDPE) or another polyethylenematerial installed over a substantially rigid and incompressible steelor other metal pipe core having an outer diameter that is the same orslightly larger than a normal inside diameter of the polyethylene pipeor tube when measured in a relaxed state at ambient temperature. Thepolyethylene pipe or tube is, for example, a HDPE 3408 material formedof virgin PE 3408 resin as specified in ASTM D3350 with UV protection,and the pipe is produced to ASTM A-3408. The metal pipe core can beferrous or nonferrous pipe.

According to one aspect of the invention, the wherein the elongatedpolyethylene pipe or tube is pre-heated to expand its inside diameterand soften the material. The elongated polyethylene pipe or tube isslid, possibly under some axial force or pressure, over the piling orpipe. Sliding the elongated polyethylene pipe or tube over the largerdiameter core further expands its inside diameter to larger than itsrelaxed state measurement. After installation over the core, theelongated polyethylene pipe or tube is permitted to relax and contractor “shrink” radially, whereby the polyethylene pipe or tube radiallycompresses the outside of the substantially rigid and incompressiblecore pipe. When pre-heated, the inside diameter of the polyethylene pipeor tube contract or shrinks radially upon cooling to form a compressionfit around the rigid core.

According to one aspect of the invention, the core is alternatively awooden post for use as a pile.

According to another aspect of the invention, when the wood piling orsteel pipe is to be used as a piling, the polyethylene pipe or tube isextended to or past the ends of the core pipe, and the open ends of thepolyethylene pipe or tube are closed by plastic caps that are thermalfusion plastic welded or chemically welded in a water-tight manner. Whenthe steel pipe is to be used in a string to form a pipe line, the steelpipe is extended beyond the polyethylene pipe or tube to expose shortlength of the core pipes, adjacent pipes are steel welded or otherwisejoined, and “clamshell” portions of polyethylene material is chemicallyor thermal fusion welded between the polyethylene pipe or tube ofadjacent pipes in a water-tight manner.

Other aspects of the invention are detailed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an end view that illustrates the present invention by exampleand without limitation embodied as a composite structural device formedof an elongated substantially cylindrical hollow pipe core materialhaving an outer peripheral skin formed of a sleeve of seamless extrudedor seam welded plastic pipe that is adhered to the core material byfriction caused by radial compression;

FIG. 2 is an end view that illustrates the composite structural deviceof the present invention wherein the elongated substantially cylindricalcore is a solid core, such as a solid wooden or plastic pile;

FIG. 3 is a flow diagram that illustrates the process of the inventionwhereby the composite structural device of the present invention isformed;

FIG. 4 illustrates the mechanical process of the invention prior toassembly of the core and plastic pipe sleeve;

FIG. 5 illustrates one embodiment of the invention at an intermediatestage of assembly of the core and plastic pipe sleeve;

FIG. 6 illustrates an alternative embodiment of the invention at anintermediate stage of assembly of the core and plastic pipe sleeve;

FIG. 7 illustrates one embodiment of the invention at an end stage ofassembly of the core and plastic pipe sleeve;

FIG. 8 illustrates an embodiment of the invention wherein two or morecomposite devices of the invention are joined by lengthwise joints intoa longer string of such devices;

FIG. 9 illustrates one embodiment of the invention wherein a metal nosecone is provided in the exposed portion of the core to operate as ameans for protecting and sealing the annular joint developed at theinterface between the core and plastic pipe sleeve when the compositestructural device is driven lengthwise into the earth or another medium;

FIG. 10 illustrates the nose cone of the invention illustrated in FIG. 9being collapsed about a portion of the exposed portion of the core andextending over a lip portion of the plastic pipe sleeve plastic pipesleeve, whereby the nose cone protects the entrance to an annular jointat the interface between the core and plastic pipe sleeve;

FIG. 11 illustrates one embodiment of the invention that is useful forthe composite structural device being used as a piling wherein aquantity of supplemental rub strips are welded to the outer wall surfaceof the plastic pipe sleeve as a means for protecting the integrity ofthe plastic pipe sleeve in high wear applications; and

FIG. 12 illustrates another embodiment of the invention that is usefulfor the composite structural device being used as a piling wherein atraveler is provided over the outer wall surface of the plastic pipesleeve as a means for protecting the integrity of the plastic pipesleeve in high wear applications.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In the Figures, like numerals indicate like elements.

FIG. 1 is an end view that illustrates the present invention by exampleand without limitation embodied as a composite structural device formedof an elongated substantially cylindrical hollow pipe core materialhaving an outer peripheral skin formed of a sleeve of seamless extrudedor seam welded plastic pipe that is adhered to the core material byfriction caused by radial compression.

As illustrated in FIG. 1, the composite structural device 10 of theinvention is formed of an elongated substantially cylindrical metal pipecore 12 having an outer peripheral skin formed of a sleeve of seamlessextruded or seam welded plastic pipe 14. The plastic pipe sleeve 14 isadhered to the metal pipe core 12 by intersurface friction caused byradial compression that results from the plastic pipe sleeve 14 having anominal inside diameter ID_(p) before installation that is thesubstantially same or smaller than an outside diameter OD_(c) of themetal pipe core 12, and a “memory” or tendency to return or “shrink” toits nominal inside diameter ID_(p), after installation.

According to one embodiment of the invention, the metal pipe core 12 isa ferrous material, such as any grade of carbon or stainless steel,ductile iron, a nickel-based ferrous material such as Inconel® whichrefers to a family of trademarked high strength austeniticnickel-chromium-iron (NiCrFe) alloys that contain high levels of nickeland can be thought of as super-stainless steels having exceptionalanti-corrosion and heat-resistance properties for use in a variety ofextreme applications including navy boat exhaust ducts, submarinepropulsion motors, undersea cable sheathing, heat exchanger tubing andgas turbine shroud rings, as well as other ferrous materials. Accordingto other embodiments of the invention, the metal pipe core 12 is anonferrous material, such any grade of aluminum or aluminum alloy.

According to one embodiment of the invention, the plastic pipe sleeve 14is formed of a thermoplastic material that is weldable in a water-tightmanner by means of thermal fusion plastic welding or chemical welding(hereinafter “plastic welding”). For example, according to oneembodiment of the invention, the plastic pipe sleeve 14 ispressure-rated thermoplastic pipe, such as polyethylene pipe (PE)including high-density polyethylene (HDPE), ultrahigh molecular weight(UHMW) PE and cross-linked PE plastic piping materials. Suchthermoplastic materials are widely used because of their chemicalresistance, freeze resistance, impact and abrasion resistance, stressabsorption properties, and weathering capabilities including resistanceto sunlight and ultraviolet (UV) attack, but also because of their lowcost and, because these materials are chemically inert, they are evenapproved for use around fish and plants. These thermoplastic pipematerials are commercially available in low, medium and high density(Type II and Type III). Their low cost is due in part to theirfabrication which is usually by extrusion of seamless pipe, but may beby rolled sheets with heat-fused joints that result in an exceptionallysmooth inner surface within the pipe.

Ultrahigh molecular weight (UHMW) PE and cross-linked PE plastic pipingmaterials are a relatively new developments in PE piping. The UHMW PEhas considerably higher resistance to stress-cracking but is more costlythan conventional PE piping material. It offers an extra margin ofsafety when used in sustained pressure conditions in comparison withpipe made from lower molecular weight resin. It is suitable for certainapplications in the chemical industry where stress-cracking resistancehas been a limiting factor for the conventional PE pipe.

Cross-linked PE piping material, when compared to ordinary PE pipe,displays greater strength, higher stiffness and improved resistance toabrasion and to most chemicals and solvents at elevated temperatures upto 95 degrees C. (203 degrees F.). Pipe made from cross-linked PE alsohas high-impact resistance even at sub-zero temperatures. It is used inapplications too severe for ordinary PE pipe and is strong enough forjoining by threading.

High-density polyethylene (HDPE) piping material is made from acrystalline resin or polymer known for its flexibility, toughness andchemical resistance. These features make HDPE pressure pipe well suitedfor those applications or industries requiring a pipe that is strong,durable, corrosion resistant and yet at the same time flexible enough tobe assembled and installed in the most inaccessible and harshenvironments. HDPE pressure pipe is the preferred pipe of choice formost trenchless technologies like pipe bursting and horizontal directiondrilling. HDPE pressure pipe is a common choice for projects requiring apiping solution that must be able to cope with extreme pressure loadsunder harsh conditions.

HDPE 3408 is one example of high-density polyethylene (HDPE) highpressure piping material. HDPE 3408 is a premium quality, high density,extra high molecular weight (EHMW) black polyethylene pipe that isspecifically intended for the rigors of the oil field. It is producedfrom virgin PE 3408 resin as specified in ASTM D3350 and contains carbonblack for superior resistance to UV degradation. HDPE 3408 pipe ismanufactured in accordance with the ASTM A-3408 standard, as well asAWWA, ASTM, FM, CSA, BNQ, and NSF Standards. HDPE 3408 pipe offersoutstanding environmental stress crack resistance, the highest chemicalresistance of any polyethylene pipe and high impact resistance, and ismade tough enough to easily handle pressure fluctuation and line surges.HDPE 3408 pipe diameters are known to range from ½ inch to 6 inchcoiled, and ½ inch to at least 54 inch straight lengths.

HDPE 3408 black polyethylene pipe is manufactured to withstand extendedoutdoor storage and above-ground use in most climates by dispersion offine carbon black which is the most effective additive for protectingpolyethylene from the effects of weathering. By example and withoutlimitation, one commercially available brand of HDPE 3408 blackpolyethylene pipe includes a minimum of 2 percent finely dispersedcarbon black. Such UV-stabilized HDPE pipe can be exposed for longperiods of time without decline in performance level. Weatheringcapabilities of HDPE pipe also include freeze resistance.

The virgin PE 3408 is a microbiological resistant polyethylene resinthat offers optimum chemical resistance so that pipe made of HDPEPE-3408 easily withstands high acid soils and fertilizers and is capableof handling the transfer of extremely corrosive materials, e.g.,industrial wastes and chemical acids. Because HDPE is resistant to abroad range of chemicals in varying degrees of concentration, sunlightand UV attack, as well as being approved for use with fish and plants,it is known as an excellent application for leach pads, wastewaterponds, landfills, aquaculture systems, landfill covers, secondarycontainment and tanks.

HDPE PE 3408 pressure pipe is manufactured from a high densitypolyethylene polymer of a molecular structure having much longer chainswith fewer side branching when compared to ordinary polyethylene pipingmaterial so that HDPE PE 3408 pressure pipe has greater density and acrystallinity level in the range of 85 percent. As a rule, when thedensity increases, the stiffness, harness, strength, heat distortionpoint, and ability to transmit gasses increases. When density decreases,impact strength and stress crack resistance increases, where stresscracking is a surface change that polyethylene undergoes when exposed tooils, gasoline and other hydrocarbons. HDPE PE 3408 pressure pipe israted at a density range of 0.941 to 0.965 gr/cc and is thereforesuperior in stiffness, hardness and strength which causes it to be idealfor pressure applications. Most importantly, HDPE PE 3408 pressure pipecan handle greater pressures under extremely corrosive conditions. Forexample, HDPE PE 3408 pressure pipe can be buried to great depths andcan tolerate severe soil strain and soil movements (rise or settlement),and is even seismically qualified in laboratory studies and field provento be earthquake tolerant.

Table 1 illustrates typical physical properties of high densitypolyethylene pipe, as provided by Chevron Phillips Chemical Company.This list of typical physical properties shown in Table 1 is intendedfor basic characterization of the material and does not representspecific determinations of specifications. The physical propertiesvalues reported in Table 1 were determined on compression moldedspecimens prepared in accordance with Procedure C of ASTM D 1928 and maydiffer from specimens taken from pipe. In some instances, testing mayhave been discontinued because no failures and no indication of stresscrack initiation occurred.

TABLE 1 Property Specification Unit Nominal Value Material DesignationPPI/ASTM PE 3408 Material Classification ASTM D-1248 III C 5 P34 CellClassification ASTM D3350-99 345464C -Density (3) ASTM D-1505 gm/cm30.955 -Melt Index (4) ASTM D-1238 gm/10 min. 0.11* (216 kg/190 C.) -FlexModulus (5) ASTM D-790 psi 135,000 -Tensile Strength (4) ASTM D-638 psi3,200 PENT (6) ASTM F-1473 Hours >100 -HDB @73_(i) F (4) ASTM D-2837 psi1,600 -HDB @ 140 Deg F ASTM D-2837 psi 800 -U-V Stabilizer (C) ASTMD-1603 % C 2.5 Hardness ASTM D-2240 Shore “D” 65 Compressive Strength(yield) ASTM D-695 psi 1,600 Tensile Strength @ Yield ASTM D-638(2″/min.) psi 3,200 (Type IV Spec.) Elongation @ Yield ASTM D-638 %,minimum 8 Tensile Strength @ Break ASTM D-638 psi 5,000 (Type IV Spec.)Elongation @ Break ASTM D-638 %, minimum 750 Modulus of Elasticity ASTMD-638 psi 130,000 PENT (6) ASTM F-1473 Hours >100 (Cond. A, B, C: Mold.Slab) ASTM D-1693 Fo, Hours >5,000 (Compressed Ring-pipe) ASTM F-1248Fo, Hours >3,500 Slow Crack Growth Battelle Method Days to Failure >64Impact Strength (IZOD) ASTM D-256 In-lb/in notch 42 (.125O Thick)(Method A) Linear Coefficient of Thermal ASTM D-696 in/in/F. 1.2 × 10-4Expansion Thermal Conductivity ASTM D-177 BTU-in/ft²/hrs/ 2.7 degrees F.Brittleness Temp. ASTM D-746 degrees F. <−180 Vicat Soft. Temp. ASTMD-1525 degrees F. 257 Heat Fusion Cond. ASTM D-1525 @ psi degrees F. 75@ 400 *Average Melt Index value with a standard deviation of 0.01

Medium density polyethylene is an alternative piping material for theplastic pipe sleeve 14 of the invention. According to one embodiment ofthe invention, a minimum carbon black content of 2.5 percent providesexcellent protection from UV rays and harsh weather conditions. MediumDensity Polyethylene has a 20 year average life and puncture and tearstrengths that far exceed common polyethylene or vinyl films. MediumDensity Polyethylene is commonly used for larger ponds, includinglagoons, canal liners, fire ponds, remediation liners, cargo covers, oilfield pit liners, silage covers, outdoor covers, brine ponds, minetrailing ponds, interim landfill caps, leachate collection ponds.

Polyethylene piping material is quickly and easily joined and installedby using the heat fusion method which produces a solid, leak-proof jointthat is as strong as the base pipe.

While the molecular structure of HDPE pipe gives it certain advantagesover other plastic pipe for the plastic pipe sleeve 14 of the invention,the only absolute requirement of the invention is the plastic pipesleeve 14 must expand radially to admit the core 12 thereinto, andthereafter radially contract to bring an inner wall surface IW_(p) ofthe plastic pipe sleeve 14 into a compressive contact with an outer wallsurface OW_(c) of the core 12. Accordingly, different plastic pipes arealternatively substituted for the HDPE pipe, HDPE PE 3408 pressure pipe,UHMW PE pipe, medium density polyethylene pipe, cross-linked PE pipe orother polyethylene piping materials described herein.

According to one embodiment of the invention, the plastic pipe sleeve 14is a acrylonitrile-butadiene-styrene (ABS) pipe, which is a copolymermade from the three monomers described in the heading, and contains atleast 15 percent of acrylonitrile. ABS is a rigid plastic with goodimpact resistance at lower temperatures down to −40 degrees C. (−40degrees F.) and can be used at temperatures up to 80 degrees C. (176degrees F.). ABS is utilized mainly for drain-waste-ventilation (DWV)pipe and fittings but it is also used in solvent cement for installingpipe in various applications. ABS pipe can be joined by solvent weldingor threading. A new development in the ABS-DWV piping industry is theco-extruded foam-core ABS pipe that is also useful for practicing theinvention. ABS-DWV has a foam core sandwiched between solid skins and isuseful as sewer, conduit and duct pipe. The foam-core ABS-DWV pipe haslower resin requirements than conventional ABS pipe.

According to another embodiment of the invention, the plastic pipesleeve 14 is a polybutylene (PB) pipe, which has practically no creepand has excellent resistance to stress cracking. Polybutylene plasticpipe is flexible, and in many respects similar to Type III polyethylene,but is stronger. Polybutylene plastic piping is relatively new, and thusfar its use has been limited to the conveyance of natural gas and towater distribution systems. High temperature grade polybutylene plasticpipe can resist temperatures of 105 to 110 degrees C. (221 to 230degrees F.).

According to another embodiment of the invention, the plastic pipesleeve 14 is a polypropylene (PP) piping, which is the lightest-weightplastic material, having a density of 0.90 g/cm³, and generally hasbetter chemical resistance than other plastics. Polypropylene is used insome pressure piping applications, but its primary use is in lowpressure lines. Polypropylene plastic pipe is used for chemical (usuallyacid) waste drainage systems, natural-gas and oil-field systems, andwater lines. The maximum temperature for non-pressure polypropylenepiping is 90 degrees C. (194 degrees F.). Pipe lengths are joined byheat fusion, threading, e.g., with heavy pipe, and mechanical sealdevices.

According to other embodiments of the invention, the plastic pipe sleeve14 is another thermoplastic used in the manufacture of pipe, includingpoly(vinylidene chloride), poly(vinylidene fluoride), cellulose acetatebutyrate (CAB), acetal homopolymer resins, rubber-modified systems,polytetrafluoroethylene (PTFE), and fluorinated ethylene-propylene (FEP)copolymer. However, these materials are relatively more expensive.

When the plastic pipe sleeve 14 is practiced using one of thethermoplastic piping options, such as polyethylene and in particularHDPE PE 3408 pressure pipe, sleeves 14 of two composite pilings 10 areeasily fusion welded together with weld joints as strong as the originalpipe whereby the thermoplastic piping is a monolithic or one piecepiping solution. This monolithic thermoplastic piping solution is idealfor corrosive applications compared to other piping materials such asgalvanized steel pipe which can wear through in time making themsusceptible to possible leaks or pressure failure. Secondly, when theplastic pipe sleeve 14 is practiced using one of the thermoplasticpiping options manufactured in accordance with the ASTM A-3408 standardor another accepted standard using virgin PE 3408 resin material inaccordance with the ASTM D3350 standard or another virgin resin materialin accordance with another accepted standard, and the metal pipe core 12is manufactured in accordance with an accepted standard, the compositestructural device 10 of the invention is fully compliant with acceptedASTM standards without further testing or certification.

FIG. 2 is an end view that illustrates the composite structural device10 of the present invention wherein the elongated substantiallycylindrical core 12 is a solid core, such as a solid wooden or plasticpile in contrast to the metal pipe core illustrated in FIG. 1. The solidcore 12 is an elongated substantially cylindrical core having an outerperipheral skin formed of the sleeve 14 of seamless extruded or seamwelded plastic pipe that is adhered to the core material by frictioncaused by radial compression.

FIG. 3 is a flow diagram that illustrates the process of the inventionwhereby the composite structural device 10 of the present invention isformed.

FIGS. 4, 5, 6 and 7 are pictorial views that illustrate the mechanicalprocess of the invention as illustrated in FIG. 3, whereby the compositestructural device 10 of the present invention is formed. FIG. 4illustrates the mechanical process of the invention prior to assembly ofthe core 12 and plastic pipe sleeve 14. FIG. 5 illustrates oneembodiment of the invention at an intermediate stage of assembly of thecore 12 and plastic pipe sleeve 14. FIG. 6 illustrates an alternativeembodiment of the invention at an intermediate stage of assembly of thecore 12 and plastic pipe sleeve 14.

In step A of the invention, an elongated substantially cylindrical core12 is selected. The core 12 may be either a solid core of the typeillustrated in FIG. 2, or a tubular pipe core of the type illustrated inFIG. 1. If the core 12 is a hollow pipe, it may be selected from anyform or grade of ferrous or nonferrous pipe material manufacturedaccording to an accepted ASTM standard, as discussed herein, and fromany length appropriate to the end-user application. When an innerdiameter of the end product is a desirable result, the pipe core 12 isselected having an inner diameter ID_(c) of the desired dimension formedby an inner wall surface IW_(c).

In step B of the invention, a plastic pipe sleeve 14 is selected fromany plastic tube or pipe material that is radially expandable withouttearing. According to one embodiment of the invention, the core 12 isselected from the family of HDPE piping materials. According to oneembodiment of the invention, the plastic pipe sleeve 14 is a pipe isproduced in accordance with ASTM A-3408 using HDPE 3408 material formedof virgin PE 3408 resin as specified in ASTM D3350 and contains carbonblack for UV protection. The plastic pipe sleeve 14 is selected having anominal inside diameter ID_(p) before installation that is the same orslightly smaller than an outside diameter OD_(c) of the selected core12.

When the plastic pipe sleeve 14 is produced by extrusion, the inner wallsurface IW_(p) is sufficiently smooth to accept the core 12 with littleor no drag. When the plastic pipe sleeve 14 is a pipe is produced inaccordance with ASTM A-3408, it has an exceptionally smooth innersurface, and any heat-fused joints offer little drag or resistancewithin the pipe to acceptance of the core 12. Accordingly, alongitudinal force F_(L) applied during installation of the plastic pipesleeve 14 onto the steel pipe or other elongated substantiallycylindrical core 12 is minimized.

Alternatively, if an outer diameter of the end product is a desirableresult, the plastic pipe sleeve 14 is selected having an outer diameterOD_(p) that, in a relaxed state prior to installation over the core 12,is the same or smaller than the desired outer diameter result, and thecore 12 is selected having an outer diameter OD_(c) that is the same orslightly larger than a normal inside diameter ID_(p) of the plastic pipesleeve 14.

Accordingly to one embodiment of the process of the invention, in a stepC the plastic pipe sleeve 14 is optionally pre-warmed to a temperatureabove ambient but below a melting point of the sleeve material, e.g.below 240 degrees F. when the plastic pipe sleeve 14 is formed of HDPEPE 3408 pipe. Pre-warming the plastic pipe sleeve 14 is optional, butsuch pre-warming reduces the force F_(L) applied during installation ofthe plastic pipe sleeve 14 onto the steel pipe or other elongatedsubstantially cylindrical core 12, as discussed herein. Selection ofpre-warming, and if present, pre-warming temperature is also a functionof the “stretchability” of the plastic pipe sleeve 14. All relevantdimensions being equal, a plastic pipe sleeve 14 of a more stretchablematerial is more easily installed over a core 12 than a plastic pipesleeve 14 of a less stretchable material. Thus, a plastic pipe sleeve 14of a less stretchable material is optionally pre-warmed to a highertemperature than a plastic pipe sleeve 14 of a more stretchable materialto reduce the force F_(L) applied during installation of the plasticpipe sleeve 14 onto the core 12.

If present, pre-warming of the plastic pipe sleeve 14 may be practicedusing any means available. For example, pre-warming of the plastic pipesleeve 14 is practiced by immersion for a period of time in a liquidsuch as oil or water heated to a temperature above ambient but below amelting point of the sleeve material, or immersion in a similarly heatedenvironment such as a steam bath. Pre-warming of the plastic pipe sleeve14 is alternatively practiced by open flame, as produced by a gas-firedtorch, or radiant heat from a bed of hot coals, as long as the plasticpipe sleeve 14 is not warmed above the melting point of the sleevematerial. Pre-warming is alternatively practiced by allowing the plasticpipe sleeve 14 to stand or lie in a natural warming environment, forexample, out doors in warm weather or under the direct rays of the sun.According to one embodiment of the invention, pre-warming is practicedby installing the plastic pipe sleeve 14 in an oven or other warmingdevice 16 (hereinafter warming device 16) sized to accommodate theselected length L_(p) of the section of plastic pipe sleeve 14 to beinstalled on the elongated core 12, which may be the same or less thanthe overall length L_(c) of the elongated core 12. The warming device 16is, for example, a tubular propane-fired oven, a natural gas or othergas-fired oven, an electric current oven such as an induction, arc orresistance oven, or an oven operated with a different heat source. Thewarming device 16 or other pre-warming means does not even have to heatthe entire plastic pipe sleeve 14 to a uniform temperature throughout.Rather, one side can be pre-warmed to a much higher temperature than anopposite side, as in sun warming of a plastic pipe sleeve 14 lying onthe ground. The invention may be practiced using nonuniform pre-warmingat least, first, because pre-warming of the plastic pipe sleeve 14 isnot a requirement of the installation process, second, because partialpre-warming is effective for softening and making more pliable at leastthat portion of the plastic pipe sleeve 14 that is so pre-warmed, third,because heat conduction through the material tends to equalize thetemperature throughout the plastic pipe sleeve 14.

According to one embodiment of the invention, when the plastic pipesleeve 14 is high-density polyethylene (HDPE) pipe, the plastic pipesleeve 14 is pre-warmed to about 150 degrees F. which is above ambientbut well below a melting point of the HDPE sleeve material.

In an optional step D of the invention, a lubricant 18 is applied to theinner wall surface IW_(p) of the plastic pipe sleeve 14, either beforeor after pre-warming. The lubricant 18 operates as a means forovercoming frictional forces between the core 12 and plastic pipe sleeve14 as a further optional means for minimizing or at least reducing theforce F_(L) applied during installation of the plastic pipe sleeve 14onto the steel pipe or other elongated substantially cylindrical core12, as discussed herein. The lubricant 18 is selected to avoid chemicalinteraction with either the material of the core 12 or the material ofthe plastic pipe sleeve 14. For example, if the plastic pipe sleeve 14is selected to be HDPE pipe, carbon or petroleum based products areavoided for use as the lubricant 18 because such products are known toattack the cellular matrix of polyethylene piping materials and to causesoftening of the materials over time, whereby the plastic pipe sleeve 14tends to loose its pressure rating and rupture under load. According toone embodiment of the invention, the lubricant is instead selected to bea light vegetable oil.

According to one embodiment of the invention wherein the lubricant 18 isa light vegetable oil applied to the inside wall surface IW_(p) of theplastic pipe sleeve 14, the plastic pipe sleeve 14 is pre-warmed to atemperature that is at least slightly below the cook-off temperature ofthe vegetable oil of about 160 degrees F. Accordingly, the plastic pipesleeve 14 is pre-warmed to about 150 degrees F. which is well aboveambient but still slightly below the cook-off temperature of thevegetable oil lubricant 18.

According to one alternative embodiment of the process of the inventionillustrated in FIG. 3, the lubricant 18 is optionally applied to anouter wall surface OW_(c) of the core 12, either instead or incombination with the lubricant 18 that is applied to the inner wallsurface IW_(p) of the plastic pipe sleeve 14 in optional step D of theinvention. As described above, the lubricant 18 operates as a means forovercoming frictional forces between the core 12 and plastic pipe sleeve14 as a further optional means for reducing the force F_(L) appliedduring installation of the plastic pipe sleeve 14 onto the steel pipe orother elongated core 12, as discussed herein. As is further discussedherein, the lubricant 18 is selected to avoid chemical interaction witheither the material of the core 12 or the material of the plastic pipesleeve 14.

According to another alternative embodiment of the process of theinvention illustrated in FIG. 3, the lubricant 18 is optionally appliedto the outer wall surface OW_(c) of the core 12 during installation ofthe plastic pipe sleeve 14. Accordingly, the lubricant 18 is applied tothe outer wall surface OW_(c) of the core 12 as or immediately beforeentry into the plastic pipe sleeve 14 by means of a lubricant dispenser19 provided adjacent to where the core 12 meets the plastic pipe sleeve14.

Preferably, the core 12 is not pre-warmed so that any thermal expansiondue to such pre-warming is avoided.

In step E of the invention, a first open end or mouth 20 of the plasticpipe sleeve 14 is exposed. If the plastic pipe sleeve 14 is pre-warmedin a warming device 16 of a type having doors 22, the mouth 20 of theplastic pipe sleeve 14 is positioned in the warming device 16 such that,when the doors 22 are opened, the mouth 20 is exposed and available forinstallation over the core 12. According to one embodiment of theinvention, the plastic pipe sleeve 14 optionally remains in the warmingdevice 16 or other warming device as a means for retaining thetemperature to which it has been pre-warmed. Alternatively, the plasticpipe sleeve 14 is removed from the warming device 16 prior toinstallation over the core 12.

In step F of the invention, a longitudinal axis A_(c) of the core 12 isinitially aligned with a longitudinal axis A_(p) of the plastic pipesleeve 14, whether the plastic pipe sleeve 14 remains in the warmingdevice 16, or is removed previously therefrom. For example, the core 12and plastic pipe sleeve 14 are both supported on a linear array ofsubstantially horizontal rollers R_(H) that extends continuously from adistance in front of the oven door 20 up to and through the oven door 20into the oven or other warming device 16 and extends substantially to aback wall 24 of the warming device 16 opposite the door 20, whereby theouter wall surface OW_(c) of the elongated core 12 and an outer wallsurface OW_(p) of the plastic pipe sleeve 14 are supported on a plane Pdefined by an operational surface of the horizontal rollers R_(H) withthe plastic pipe sleeve 14 installed in the warming device 16 where itis pre-warmed to the selected temperature, and with the elongated core12 positioned outside the warming device 16 before the door 20. Lineararrays of rollers R_(H) for such support are well-known in the pipemanufacturing arts as well as other material movement arts and aregenerally commercially available. Some commercially available systems ofrollers R include two side-by-side linear arrays of rollers R with asecond array being inclined relative to a first array such as to form anangle or “V” there between, whereby the core 12 and plastic pipe sleeve14 are forced into mutual axial alignment. Alternatively, a block orstop is provided on one side of the array of horizontal rollers R_(H) asa guide for aligning the core 12 and plastic pipe sleeve 14. Accordingto one embodiment of the invention, a linear array of vertical rollersR_(V) is provided beside the linear array of horizontal rollers R_(H) tooperate as a means for substantially horizontally aligning thelongitudinal axes A_(c) and A_(p) of the core 12 and plastic pipe sleeve14, while the linear array of horizontal rollers R_(H) operates as ameans for substantially vertically aligning the respective core andsleeve longitudinal axes A_(c) and A_(p).

Optionally, means are provided for radially supporting the pre-warmedplastic pipe sleeve 14 against buckling under the longitudinal insertionforce F_(L) applied during installation of the plastic pipe sleeve 14onto the core 12. According to one embodiment of the invention, one ormore additional rollers R_(A) are provided in different positions aroundthe outer periphery of the plastic pipe sleeve 14 as a means forradially supporting the pre-warmed plastic pipe sleeve 14.Alternatively, the physical constraints of one or more interior ovenwalls 26 operate as a means for radially supporting the pre-warmedplastic pipe sleeve 14.

Furthermore, a second end or foot 28 of the plastic pipe sleeve 14 issupported against longitudinal movement in a direction opposite thesleeve mouth 20. In other words, the foot 28 of the plastic pipe sleeve14 is supported against being pushed away when the longitudinal forceF_(L) applied during installation of the plastic pipe sleeve 14 onto thecore 12. For example, the foot 28 is positioned adjacent or proximate oreven in actual butted contact with a block or other stop 30 locatedintermediate the oven door 22 and the back wall 24 of the warming device16. Stop 30 is useful when the plastic pipe sleeve 14 is short ascompared with the oven length between the door 22 and back wall 24. Stop30 is also useful when the core 12 is intended to extend beyond the foot28 of the plastic pipe sleeve 14, as discussed herein. Alternatively,the foot 28 of the plastic pipe sleeve 14 is positioned adjacent orproximate or even in actual butted contact with the back wall 24 of thewarming device 16, whereby the back wall 24 operates as the stop 30.Accordingly, the core 12 and plastic pipe sleeve 14 are relativelyaligned and positioned for insertion of the plastic pipe sleeve 14 overthe core 12.

In step G of the invention, a first end or nose 32 of the core 12 isapplied to the first end or mouth 20 of the plastic pipe sleeve 14 andthe respective longitudinal axes A_(c) and A_(p) of the core 12 andplastic pipe sleeve 14 are accurately aligned. Optionally, either one orboth of the core nose 32 and the sleeve mouth 20 is provided with alead-in that operates as a means for more accurately aligning therespective longitudinal axes A_(c) and A_(p) of the core 12 and plasticpipe sleeve 14 than is provided by the manufacturing equipment duringthe initial alignment. The core 12 and plastic pipe sleeve 14 may havedifferent respective outside diameters OD_(c) and OD_(p) depending uponsuch factors as the wall thickness of the plastic pipe sleeve 14 anddegree of interference fit, i.e., radial compression, desired betweenthe core 12 and plastic pipe sleeve 14. Therefore, the respectivelongitudinal axes A_(c) and A_(p) of the core 12 and plastic pipe sleeve14 may be substantially but not accurately aligned by the horizontalrollers R_(H) and vertical rollers R_(V), if present. Also equipmenttolerances and other vagaries common to manufacturing facilities maytend to slightly misalign the respective longitudinal axes A_(c) andA_(p) of the core 12 and plastic pipe sleeve 14. Therefore, according toone embodiment of the invention, when the core 12 is a pipe manufacturedaccording to an accepted ASTM standard, as discussed herein, the nose 32is normally provided with a 33 degree bevel nominally used in buttwelding pipe. This bevel operates as a lead-in 34 for accuratelyaligning the respective longitudinal axes A_(c) and A_(p) of the core 12and plastic pipe sleeve 14 and thereafter guiding the nose 32 of thecore 12 into the interior of the plastic pipe sleeve 14. Stateddifferently, the lead-in 34 on the nose 32 operates to align thelongitudinal axis A_(p) of the plastic pipe sleeve 14 with thelongitudinal axis A_(c) of the core 12 and further to guide the plasticpipe sleeve 14 onto the core 12. When the core 12 is a solid core of thetype illustrated in FIG. 2, the lead-in 34 is optionally cut on the nose32. Alternatively, a lead-in 36 is provided on the plastic pipe sleeve14 as an internal bevel around the mouth 20. The angle and depth of therespective lead-ins 34, 36 is selected as a function of several factors,including: the relative outside diameter OD_(c) of the core 12; theinside diameter ID_(p) of the plastic pipe sleeve 14; the sleeve wallthickness, i.e., difference of the inside and outside diameters ID_(p),OD_(p) of the plastic pipe sleeve 14; the initial alignment provided bythe manufacturing equipment; as well as other factors affectingalignment. The angle and depth of the respective lead-ins 34, 36, ifpresent, is selected also as a function of the degree of softening or“stretchability” of the plastic pipe sleeve 14 as provided by thematerial selected and, if present, the optional pre-warming provided instep C of the process.

In step H of the invention, the longitudinal force F_(L) is applied as ameans for driving the core 12 into the warming device 16 and theinterior of the plastic pipe sleeve 14. The applied longitudinal forceF_(L) is sufficient for driving the core 12 into the plastic pipe sleeve14 while simultaneously expanding the inside diameter ID_(p) of theplastic pipe sleeve 14 sufficiently to receive the outside diameterOD_(c) of the core 12. Because the core 12 is relatively rigid andsubstantially incompressible, the plastic pipe sleeve 14 expands duringassembly with the core 12, and the core 12 does not compress. Theapplied longitudinal force F_(L) necessary for installation of theplastic pipe sleeve 14 over the core 12 is as a function of severalfactors, including: the inside diameter ID_(p) of the plastic pipesleeve 14 relative to the outside diameter OD_(c) of the core 12,whether the lubricant 18 is applied to one or both of the core 12 andplastic pipe sleeve 14; and the “stretchability” of the plastic pipesleeve 14 as provided by the material selected and, if present, thedegree of softening resulting from the optional pre-warming provided instep C of the process, as well as the length L, of the plastic pipesleeve 14 to be installed as intersurface frictional forces increasewith increased intersurface area.

The longitudinal force F_(L) is supplied by any practical means to asecond end or tail 38 of the core 12 opposite from the first end or nose32. By example and without limitation, an electric, pneumatic orhydraulic other mechanical ram 40 is applied to the foot 30 of the core12 to supply the longitudinal force F_(L). Other means for applying thelongitudinal force F_(L) are also contemplated and are considered to beequivalent. For example, the longitudinal force F_(L) is alternativelyapplied by gripping the tail 38 or outside wall OW_(p) of the core 12and pulling or dragging the core 12 into the warming device 16 and theplastic pipe sleeve 14. As the longitudinal force F_(L) is applied tothe core 12, the foot 28 of the plastic pipe sleeve 14 is pushed againstthe stop 30 which simultaneously applies an equal and opposite reactionforce F_(R) to the second end or foot 28 of the plastic pipe sleeve 14as a means for maintaining the position of the plastic pipe sleeve 14against slipping away under the applied longitudinal force F_(L).Substantially continuous application of the longitudinal force F_(L) tothe core 12 thereafter drives part or all of the overall length L_(c) ofthe core 12 into the plastic pipe sleeve 14.

When the lubricant 18 is present during installation, pressure generatedby the close fit of the plastic pipe sleeve 14 over the incompressiblerigid core 12 results in the mouth 20 of the plastic pipe sleeve 14having a wiping effect against the outside wall surface OW_(c) of thecore 12 that effective removes or wipes away a greater portion of thelubricant 18. However, a sufficient quantity of lubricant 18 is retainedto operate as a means for generating a thin, low friction interfacebetween the inside wall surface IW_(p) of the plastic pipe sleeve 14 andthe outside wall surface OW_(c) of the core 12 for easing theinstallation.

In tests, when the assembled composite structural device 10 of theinvention was sectioned crosswise to the longitudinal axis, no lingeringtrace of the vegetable oil lubricant 18 was detected between the insidewall surface IW_(p) of the plastic pipe sleeve 14 and the outside wallsurface OW_(c) of the core 12.

FIG. 6 illustrates an alternative embodiment of the invention whereinthe ram 40 applies the longitudinal force F_(L) to the foot 28 of theplastic pipe sleeve 14, while the stop 30 is positioned to apply theequal and opposite reaction force F_(R) to the tail 38 of the core 12.According to this optional embodiment of the invention, the plastic pipesleeve 14 is pre-warmed in the warming device 16, and after attainingthe selected temperature, is driven out of the warming device 16 andonto the core 12.

FIG. 7 illustrates a radially contracting step I of the inventionwherein the composite structural device 10 having the selected lengthL_(p) of the plastic pipe sleeve 14 installed over the elongatedcylindrical core 12 is cooled to ambient temperature as a means forradially compressing the plastic pipe sleeve 14 around the circumferenceof the outside wall OW_(p) of the core 12. As the heat in the plasticpipe sleeve 14 dissipates, as indicated by the wavy heat dissipationarrows, whereby material size “memory” of the plastic pipe sleeve 14causes the inner diameter ID_(p) to return or “shrink,” as indicated bythe inwardly radial compression arrows Rc, to its nominalcircumferential dimension after installation over the core 12 and uponreturn to ambient temperature. As a means for facilitating andaccelerating cooling of the plastic pipe sleeve 14 and causing it toshrink around the core 12, the composite structural device 10 isoptionally removed from the warming device 16 after assembly of the core12 and plastic pipe sleeve 14, unless assembly was completed outside ofthe optional warming device 16, or the warming device 16 was not used.Removal from the warming device 16 also frees the warming device 16 fora next cycle of forming the composite structural device 10.

Shrinking of the plastic pipe sleeve 14, whether through material memoryafter being stretched to admit the core 12, or through cooling afterremoval from the warming device 16, causes the plastic pipe sleeve 14 toradially contract around the outer wall surface OW_(c) of the core 12forming a high compression interface between the outer wall surfaceOW_(c) of the core 12 and the inner wall surface IW_(p) of the plasticpipe sleeve 14. The radial compression loading at the interface is as afunction of several factors, including: a difference between the insidediameter ID_(p) of the plastic pipe sleeve 14 and the outside diameterOD_(c) of the plastic pipe sleeve 14; the size memory of the materialselected for the plastic pipe sleeve 14; and the wall thickness of theplastic pipe sleeve 14. Even minimal radial compression loadingcompletely eliminates any annular separation between the core 12 andplastic pipe sleeve 14. Furthermore, as discussed herein, the process ofthe invention provides at least minimal radial compression loading thatcompletely eliminates any annular separation between the core 12 andplastic pipe sleeve 14 along substantially the entire interface betweenthe outer wall surface OW_(c) of the core 12 and the inner wall surfaceIW_(p) of the plastic pipe sleeve 14. Such minimal radial compressionloading also operates as a means for adhering the plastic pipe sleeve 14to the outer wall surface OW_(c) of the core 12 by generating africtional interface over substantially the entire intersurface area.Increasing the radial compression loading operates to increase theintersurface frictional adhesion by increasing the intersurfacefrictional forces.

Furthermore, the close or even interference fit of the core 12 andplastic pipe sleeve 14 necessitates the application of longitudinalforce F_(L) and reactive force F_(R) prevents contaminants from enteringthe intersurface area between the outer wall surface OW_(c) of the core12 and the inner wall surface IW_(p) of the plastic pipe sleeve 14.Therefore, the annular joint J_(a) developed at the interface betweenthe core 12 and plastic pipe sleeve 14 does not normally requireprotection, neither during assembly of the composite structural device10 nor during circumferential contraction of the stretched plastic pipesleeve 14 around the outer wall surface OW_(c) of the core 12, whetherthe means for circumferential contraction is cooling or other materialmemory phenomenon.

As illustrated in FIG. 7 the plastic pipe sleeve 14 does not have tocompletely cover the core 12. Rather, according to one embodiment of theinvention, a portion P_(E) at each end of the core 12 is left exposed bythe installed plastic pipe sleeve 14. The exposed portion P_(E) permitsbutt welds or other circumferential joints J_(w) between multiplecomposite pilings 10 into a longer string S of the type illustrated inFIG. 8. Thus, according to one embodiment of the invention, thecomposite structural device 10 is substantially symmetrical about aperpendicular centerline, C_(L) with the plastic pipe sleeve 14 exposinga substantially identical length of exposed portion P_(E) at both thenose 32 and tail 38 ends of the core 12.

As illustrated in FIG. 8, two or more composite devices 10 are joined bylengthwise joints J_(w) into a longer string S. Thereafter, a clam-shellunion 42 of plastic piping material of substantially the same orchemically similar type as the material selected for the plastic pipesleeve 14 is fitted over the exposed portions P_(E) of the joined cores12, including the butt weld or other lengthwise joint J_(w) betweenadjacent composite pipes or pilings 10. The clam-shell union 42 isformed of two or more semi-cylindrical portions 44 of the selectedpiping material, each of the semi-cylindrical portions 44 being sized tosubstantially fill the gap G between the plastic pipe sleeves 14 ofadjacent composite pipes of pilings 10 and further to coversubstantially the entire outer surface areas of each exposed portionP_(E) of the joined cores 12. The clam-shell portions 44 are thereafterthermal fusion plastic welded or chemically welded together in awater-tight manner (hereinafter “plastic welded”) by means of lengthwiseweld joints J_(L), to form a tube or sleeve of plastic piping materialaround and completely covering the exposed portion P_(E) of the joinedcores 12. The clam-shell portions 44 are also plastic welded to therespective plastic pipe sleeve 14 on either core 12 in circumferentialbutt weld joints J_(B). The lengthwise joints J_(w) between multiplecomposite devices 10 and both the plastic lengthwise weld joints J_(L),and the circumferential butt weld joints J_(B) are accomplished in thefield using techniques generally well-known to those of skill in therelevant art. Field welding of the cores 12 and the clam-shell union 42permits multiple composite devices 10 to be transported to a site of useand assembled and installed in place. Installation of the clam-shellunion 42 effectively seals the exposed portion P_(E) of the joined cores12 in the gap G between the plastic pipe sleeves 14 including thecircumferential butt weld joints J_(B). The clam-shell union 42 alsopermits the composite structural device 10 to manufactured in standardlengths, which reduces inventory costs.

When a non-standard or irregular length of composite structural device10 is required for a particular application, the core 12 can be cut tothe desired length and the plastic pipe sleeve 14 cut and peeled off toprovide the exposed portion P_(E) of the core 12 illustrated in FIG. 8for joining to another core 12.

When the composite structural device 10 is not terminated with a valveor other device, as when it is used as a piling rather than atransmission pipe, the exposed portion P_(E) of the core 12 isoptionally sealed with an end cap 46 formed of a material that is thesame or a compatible with the plastic material of which the plastic pipesleeve 14 is formed. The end cap 46 is plastic welded to the plasticpipe sleeve 14 in a circumferential butt weld joint J_(B). The end cap46 protects the exposed portion P_(E) of the core 12 and simultaneouslyprotects the annular joint J_(a) developed at the interface between thecore 12 and plastic pipe sleeve 14, which is the weakest part of thecomposite structural device 10.

FIG. 9 illustrates one embodiment of the invention wherein a metal nosecone 48 is provided in the exposed portion P_(E) of the core 12 tooperate as a means for protecting and sealing the annular joint J_(a)developed at the interface between the core 12 and plastic pipe sleeve14 when the composite structural device 10 is driven lengthwise into theearth or other medium E. The nose cone 48 has collar 50 from which afunnel-shaped metal skirt 52 extends. The nose collar 50 is coupled tothe core 12 in the exposed portion P_(E) adjacent to either the nose 32or tail 38 with the skirt “hanging” or extending toward the plastic pipesleeve 14. For example, a circumferential weld joint J_(w) secures thecollar 50 to the nose 32 or tail 38 of the elongated cylindrical core12. According to one embodiment of the invention, the funnel-shapedmetal skirt 52 is of similar material to the core 12 and yet thin enoughto be sufficiently weak to fail and collapse while being drivenlengthwise into the earth or other medium E, whereby the failed skirt 52collapses about the mouth 20 (or foot 28) of the plastic pipe sleeve 14and thereby protects the annular joint J_(a) developed at the interfacebetween the core 12 and plastic pipe sleeve 14, which is the weakestpart of the composite structural device 10.

According to one embodiment of the invention, the skirt 52 is flared atan angle a of about 45 degrees from the collar 50. The nose cone 48 issized such that, in combination with the location of the collar 50relative to the plastic pipe sleeve 14, the skirt 52 is at least longenough to cover the mouth 20 (or foot 28) of the plastic pipe sleeve 14upon collapse. For example, when the skirt 52 has a length L_(s), thecollar 50 of the nose cone 48 is positioned a distance D_(s) from theplastic pipe sleeve 14 that is less than or equal to (1/sqrt 2)×L_(s) or0.707×L_(s).

FIG. 10 illustrates the nose cone 48 illustrated in FIG. 9 beingcollapsed about a portion of the exposed portion P_(E) adjacent to thenose 32 (or tail 38) of the core 12 and extending over a lip portion 53of the mouth 20 (or foot 28) of the plastic pipe sleeve plastic pipesleeve 14, whereby the nose cone 48 protects against entrance of foreignmatter into the annular joint J_(a) at the interface between the core 12and plastic pipe sleeve 14.

FIG. 11 illustrates one embodiment of the invention that is useful forthe composite structural device 10 being used as a piling. Accordingly,a quantity of supplemental rub strips 54 are coupled to the outer wallsurface OW_(p), of the plastic pipe sleeve 14 as a means for protectingthe integrity of the plastic pipe sleeve 14 in high wear applications.For example, when used as a piling in a marina, heavy metal retaininghoops of a type well-known in the industry may be used to circle thecomposite structural device 10 for retaining a dock. In such anapplication, the retaining hoop and dock may both rub against theplastic pipe sleeve 14 of the composite structural device 10 as afunction of fluctuating water levels, and in particular as a function oftidal motion. The supplemental rub strips 54 are slats formed of amaterial that is the same or a compatible with the plastic material ofwhich the plastic pipe sleeve 14 is formed. The supplemental rub strips54 are plastic welded to the plastic pipe sleeve 14 in a circumferentialpattern in longitudinal alignment with the longitudinal axis A_(c) ofthe core 12. Because the supplemental rub strips 54 are provided on theouter wall surface OW_(p) of the plastic pipe sleeve 14, they forciblyspace the retaining hoop and dock away from the plastic pipe sleeve 14.The supplemental rub strips 54 wear rather than the plastic pipe sleeve14 so that the core 12 remains protected. When the supplemental rubstrips 54 sufficiently worn to be in danger of exposing the plastic pipesleeve 14 to wear, the supplemental rub strips 54 can be replaced, oradditional supplemental rub strips 54 can be plastic welded over theworn strips 54.

FIG. 12 illustrates another embodiment of the invention that is usefulfor the composite structural device 10 being used as a piling.Accordingly, a traveler 56 is provided over the outer wall surfaceOW_(p) of the plastic pipe sleeve 14 as a means for protecting theintegrity of the plastic pipe sleeve 14 in high wear applications, suchas the marina application described herein. Accordingly, the traveler 56is a length L_(T) of plastic pipe having an inside diameter ID_(T) thatis sufficiently larger than the outside diameter OD_(p) of the plasticpipe sleeve 14 to permit the traveler 56 to slide along the length L_(p)of the plastic pipe sleeve 14 without interference. Additionally, a stop58 is optionally coupled to the outer wall surface OW_(p) of the plasticpipe sleeve 14 as a means for maintaining the traveler 56 within aselected range or zone Z. The supplemental rub strips 54 illustrated inFIG. 11 is optionally provided as the stop 58, wherein the strips 54 aresufficiently thick to interfere with travel of the traveler 56.Alternatively, the stop 58 is provided as a ring sized to fit closelywith the outer wall surface OW_(p) of the plastic pipe sleeve 14 andthick enough to simultaneously to interfere with travel of the traveler56. For example, the stop 58 is a short section of thick-walled plasticpipe formed of a material that is the same or a compatible with theplastic material of which the plastic pipe sleeve 14 is formed and isplastic welded in a position that is selected to maintain the traveler56 in the selected range or zone Z. When the traveler 56 is formed of aplastic of sufficiently low density to float in water, it will float upand down with fluctuation of the water. However, the user may find ituseful to add a second stop 58 of the type described herein to operateas a means for limiting the overall motion of the traveler 56 to acontrolled zone Z, which also interferes with unusual water levels,vandals or other phenomenon removing the traveler 56 from the compositestructural device 10.

FIG. 12 also illustrates an alternative embodiment of the inventionwherein the core 12 is completely enclosed and sealed within the plasticpipe sleeve 14 and a pair of end cap plates 60 formed of a material thatis the same or a compatible with the plastic material of which theplastic pipe sleeve 14 is formed. As illustrated at the upper portion ofFIG. 12, the length L_(p) of the plastic pipe sleeve 14 is extendedbeyond the tail 38, i.e., the entire length L_(c) of the core 12, by thethickness T of the cap plates 60. The cap plates 60 plastic sized to fitwithin the inside diameter ID_(p) of the plastic pipe sleeve 14 and arewelded thereto in a circumferential butt weld joint J_(C).

Alternatively, as illustrated at the lower portion of FIG. 12, thelength L_(p) of the plastic pipe sleeve 14 is extended over the entirelength L_(c) of the core 12, but does not extend beyond the nose 32 ofthe core 12. The cap plates 60 are sized substantially the same as theoutside diameter OD_(p) of the plastic pipe sleeve 14 and are weldedthereto using the circumferential butt weld joint J_(C). The cap plates60 according to one or both of the alternative embodiments are welded tothe plastic pipe sleeve 14 and, in combination with the plastic pipesleeve 14, completely encapsulate the core 12.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.For example, materials may be substituted for the different componentsof the flexible support apparatus of the invention without departingfrom the spirit and scope of the invention. In another example, theinventor has actually practiced the process of the invention bynonuniformly pre-warming the plastic pipe sleeve 14 using a propanetorch, installing the core 12 by applying the nose 32 of a pipe-typecore 12 to the sleeve mouth 20, applied the longitudinal force F_(L) byinstalling the pipe-type core 12 over a fork of a motorized fork-liftdevice and driving the fork-lift device toward the plastic pipe sleeve14 with the sleeve foot pressed against a building wall as the stop 30for applying the reactive force F_(R) against which the longitudinalinstallation force F_(L) was operated, and allowed the compositestructural device 10 to cool in room ambient atmosphere. Therefore, theinventor makes the following claims.

1. A composite structural device, comprising: a substantiallycylindrical rigid core; and an outer peripheral skin in a radiallycompressive relationship with the core, the outer peripheral skin beingformed of a sleeve of weldable thermoplastic pipe, wherein the sleeve ofthermoplastic pipe further comprises an initial inside diameter that isnot larger than an outside diameter of the core when measured in arelaxed state prior to being assembled into the radially compressiverelationship with the core.
 2. The device of claim 1 wherein the sleeveof thermoplastic pipe further comprises an initial inside diameter thatis smaller than an outside diameter of the core when measured in arelaxed state prior to being assembled into the radially compressiverelationship with the core.
 3. The device of claim 1 wherein the sleeveof thermoplastic pipe further comprises an overall length that is lessthan an overall length of the core.
 4. The device of claim 3, furthercomprising a nose cone coupled to the core in a portion thereof exposedby the sleeve of thermoplastic pipe.
 5. The device of claim 1 whereinthe core is one of a solid cylindrical core, and a hollow pipe core. 6.The device of claim 1 wherein the sleeve of weldable thermoplastic pipefurther comprises a length of high pressure piping material.
 7. Acomposite structural device, comprising: an elongated substantiallycylindrical rigid core; and a sleeve of weldable thermoplastic pipeassembled over an outside surface of the core, the pipe having a firstrelaxed state prior to being assembled over the outside surface of thecore wherein an inside diameter thereof is smaller than an outsidediameter of the core, and a second assembled state after beingcircumferentially stretched over the outside surface of the core whereinan inside diameter thereof is substantially the same as the outsidediameter of the core.
 8. The device of claim 7 wherein the assembledstate of the sleeve further comprises the sleeve being in a radiallycompressive relationship with the core.
 9. The device of claim 7 whereinthe cylindrical rigid core further comprises one of a solid pile and ahollow pipe that is selected from ferrous pipe and nonferrous pipe. 10.The device of claim 7 wherein an end portion of the core is exposedbeyond the sleeve, and further comprising a metal nose cone secured tothe exposed end portion of the core.
 11. A composite structural device,comprising: an elongated core comprising a substantially straight, rigidand cylindrical section; an elongated tubular sleeve comprising aweldable thermoplastic material and having an inside diameter asmeasured in a relaxed state that is the same or less than an outsidediameter of the core; a longitudinal axis of the tubular sleeve beingsubstantially aligned with a longitudinal axis of the core; and thesleeve being installed over at least a portion of the core, and theinside diameter of the sleeve being simultaneously expanded tosubstantially match the outside diameter of the core.
 12. The device ofclaim 11 wherein the weldable thermoplastic of the tubular sleevefurther comprises a weldable thermoplastic material that is radiallyexpandable without tearing.
 13. The device of claim 11 wherein the corefurther comprises one of a solid pile and a hollow pipe, the hollow pipebeing one of a ferrous pipe and a nonferrous pipe.
 14. The device ofclaim 13, further comprising a lubricant between the core and thesleeve.
 15. The device of claim 14 wherein the lubricant furthercomprises a material that is substantially chemically inert relative toeach of the core and the sleeve.
 16. The device of claim 15 wherein theweldable thermoplastic material further comprises high-densitypolyethylene (HDPE) high pressure piping material.
 17. The device ofclaim 16, further comprising an end portion of the core being exposedbeyond the sleeve; and a metal nose cone secured to the exposed endportion of the core.
 18. The device of claim 1, further comprising alubricant between the core and the outer peripheral skin.
 19. The deviceof claim 7, further comprising a lubricant between the core and thesleeve in the second assembled state.